1. Field of the Invention
The invention relates to a power supplying system, more particularly to one with a delayed closing device for delayed closing of a heat-dissipating fan.
2. Description of the Related Art
Electronic equipment, such as a desktop computer or an uninterruptible power system (UPS), incorporates a power supplying system to provide electrical power needed to operate the equipment. FIG. 1 illustrates a conventional power supplying system installed in a desktop computer. When the user operates a power switch on the desktop computer to operate the latter, a power-supplying unit 1 is activated so that a 110-volt alternating current (AC) input from an electrical outlet is supplied to an input rectifying and filtering circuit 10 to obtain a rectified and filtered 300-volt direct current (DC) signal. A switching unit 11 converts the 300-volt DC signal into a .+-.150-volt square wave signal. An isolation power transformer 12 reduces the output of the switching unit 11 to .+-.5 volts or .+-.12 volts. The output of the isolation power transformer 12 is filtered and rectified by an output rectifying and filtering circuit 13 before being supplied to a heat-dissipating fan 14 and to other electronic components of the desktop computer. As such, when the power-supplying unit 1 is activated, electrical power is supplied to the various electronic components of the desktop computer to operate the latter, and the heat-dissipating fan 14 is turned on to dissipate the heat that is generated due to the operation of the power-supplying unit 1 and the desktop computer. The output rectifying and filtering circuit 13 is further connected to a pulse width modulation (PWM) control circuit 15 that, in turn, is connected to the switching unit 11. The PWM control circuit 15 controls operation of the switching unit 11 to ensure that the power-supplying unit 1 will provide a stable output. When the user operates the power switch on the desktop computer to deactivate the latter, the AC input of the power-supplying unit 1 is cut-off, thereby disabling the power-supplying unit 1. The heat-dissipating fan 14 is also turned off at this time.
The following drawback arises from the aforementioned design: When the power-supplying unit 1 is turned off abruptly after operating for a period of time, a continued rise in the ambient temperature of the electronic components of the power-supplying unit 1 and the desktop computer will be experienced. Because the heat-dissipating fan 14 is already turned off, heat cannot be dissipated immediately, thereby resulting in prolonged exposure of the electronic components of the power-supplying unit 1 and the desktop computer to high ambient temperature conditions. This can result in shorter service lives for the electronic components of the power-supplying unit 1 and the desktop computer and in lower reliability.
FIG. 2 illustrates a conventional power supplying system for an ATX personal computer. Unlike the power supplying system of FIG. 1, the power-supplying unit 2 is further connected to a stand-by power source 23 and a remote switching control circuit 24. The stand-by power source 23 includes a switching and isolating circuit 230 and an output circuit 231. When the power-supplying unit 2 is activated, aside from processing the AC input for supplying the electrical power needed to operate the heat-dissipating fan 22 and the various electronic components of the ATX personal computer, the power-supplying unit 2 further provides the AC input to the stand-by power source 23. The stand-by power source 23 provides electrical power needed to operate the remote switching control circuit 24, and is connected to the motherboard (not shown) of the ATX personal computer. The motherboard is connected to a remote switch (not shown), such as a keyboard or a modem. When the remote switch input is at a high logic state, the remote switching control circuit 24 will control the PWM control circuit 210 of the power-supplying unit 2 to a remote OFF state, whereby the power-supplying unit 2 ceases to supply electrical power to the various electronic components of the ATX personal computer, and the heat-dissipating fan 22 is turned off. The stand-by power source 23 continues to operate at this time to supply the electrical power needed by the remote switching control circuit 24. When the remote switch input changes to a low logic state, the remote switching control circuit 24 will control the PWM control circuit 210 of the power-supplying unit 2 to a remote ON state, whereby the power-supplying unit 2 resumes the supply of electrical power to the various electronic components of the ATX personal computer, and the heat-dissipating fan 22 is once again turned on. The conventional power-supplying system of FIG. 2 has the following drawback during use: When the remote switch is activated to operate the power-supplying unit 2 in the remote OFF state, the power-supplying unit 2 ceases to generate electrical power for activating the heat-dissipating fan 22. Thus, a continued rise in the ambient temperature of the electronic components of the power-supplying unit 2 and the ATX personal computer will be experienced at the instant of operating the power-supplying unit 2 in the remote OFF state. This situation is aggravated due to the continued operation of the stand-by power source 23. Because the heat-dissipating fan 22 is already turned off, heat cannot be dissipated immediately, thereby resulting in prolonged exposure of the electronic components of the power-supplying unit 2 and the ATX personal computer to high ambient temperature conditions that can lead to shorter service lives for the electronic components of the power-supplying unit 2 and the ATX personal computer and lower reliability.